When partial painting is performed on an automobile brought in for repair, it is necessary to perform matching of a color (color-matching) of a repair paint in accordance with a paint color of a painting object portion of a repair vehicle.
Automobile manufacturers specify color codes for each automobile and provide information regarding mixed paints and mixing values of paints used for painting. Paint manufacturers provide, for each of the specified color codes, information (master color data) regarding paints to be mixed (paint codes), a mixing value (mixing ratio) of each mixed paint, and the like for preparation of the repair paint by use of paints manufactured and sold by each paint manufacturer.
Meanwhile, there are various methods of storing and using a vehicle by vehicle purchasers, and aged deterioration of painting of the repair vehicle differs for each vehicle and each portion thereof. In addition, in some cases, there is a difference in painting of the vehicle from a manufacturing stage due to differences in a painting method, a painting environment, and the like at an automobile manufacturing line (so-called lot-to-lot variation). As described above, since a paint color on the repair vehicle varies, even if the color code of the automobile is the same, it is not possible to prepare a repair paint conforming to the painting object portion of the repair vehicle merely by blending the paints in accordance with the master color data provided by the paint manufacturer.
Accordingly, even if it is possible to prepare a repair paint which is approximate to the paint color of the repair vehicle to a certain extent by performing blending in accordance with the master color data, it is generally necessary to perform a color-matching operation for each painting object portion of the repair vehicle. Conventionally, this color-matching operation has been performed depending on experience and intuition of an operator while using a color sample book. In recent years, however, there are cases where a colorimeter is introduced to perform the color-matching operation. Several paint manufacturers have provided color-matching support systems with a computer color searching (CCS) function or a computer color matching (CCM) function.
In a presently provided color-matching support system, a large number of pieces of master color data is put into a database, and master color data for which a color difference from colorimetric data (for example, L*a*b* value) of the repair vehicle measured by the colorimeter is the smallest is retrieved and displayed (for example, see paragraph [0038] of Patent Literature 1). In many cases, however, painting cannot be performed without color-matching, merely by retrieving and displaying the master color data for which the color difference is the smallest. To address such a problem, the paint manufacturers are trying to enrich the database by creating a plurality of color variations made by slightly changing the color of one color code, and registering these variations in the database as variations that can be used for painting on the repair vehicle, such that a candidate for a color that minimizes the color difference is selected as much as possible. As long as a search target is limited to information registered in the database, however, the problem that the paint conforming to the painting object portion of the repair vehicle is not always retrieved and displayed cannot be solved. For this reason, the operator's color-matching operation has not been sufficiently supported, and at a painting site, the operator often had to find a paint and a color-matching amount to be added from among many paints, depending on his/her experience and intuition.
In addition, a painting state changes according to a painting method such as a distance between a spray gun used for painting and the painting object portion, and speed at which the spray gun is moved, a painting tool used for painting, and painting skill, a habit, and the like of the operator. Accordingly, even if exactly the same paint is used, there will be a difference in a shade and a color tone after painting is performed. It is practically impossible to prepare a repair paint that can deal with all of the above-mentioned matters and put such a repair paint in a database. In the color sample book used at the painting site, painting plates prepared by the paint manufacturer on the basis of the mixed paints and the mixing values of the color codes. Since, however, the painting method by the paint manufacturer and the painting environment are not the same as those at each painting site, it is not always possible to reproduce the same shade and color tone expressed in the color sample book. For this reason, the operators' color-matching operation has not been sufficiently supported, and at the painting site, the operator often had to find a paint and a color-matching amount to be added from among many paints, depending on their experience and intuition.
Currently applicable colorimeters irradiate the painting object portion with light at constant luminance to measure its reflected light. Since, however, reflectance or absorptance of light varies depending on an object color, if the luminance is kept constant, an original color of the painting object portion cannot be measured accurately. In particular, a luster pigment (luster material) such as an aluminum flake pigment (metallic painting) and a pearl pigment (pearl painting, mica painting) is often added to a paint for an automobile, and these additives produce multiple reflection gloss due to difference in refractive index. Accordingly, the original color of the painting object portion cannot be measured accurately if the color is measured always at a constant luminance.